1. Field of the Invention
The present invention relates to drilling fluids utilized in the drilling of subterranean oil and gas wells, and more particularly to a filtration control additive for use in invert emulsion drilling fluids and preparing water-in-oil, emulsion-type drilling fluids; the method of preparation of the additive, and the method of their use in drilling such wells.
2. Description of the Prior Art
As is known in the art, a rotary system is the most common form of drilling subterranean wells, especially those to obtain hydrocarbons from relatively deep, producing formations. The rotary system depends upon rotation of a lengthy column of drill pipe, to the bottom of which is attached a multifaced drilling bit which serves to cut into the earth formation. As the drilling continues, the cuttings from the drilling bit accumulate in the well and must be removed in order to continue the drilling. A drilling fluid is commonly used to carry such cuttings to the surface for removal to allow the bit to continue its functioning. The bottom of the hole thus formed must be kept clean and free of cuttings at all times in order to facilitate efficient drilling. It is also known that drilling systems other than the aforesaid rotary system are sometimes employed in drilling operations; however, all such systems still require a drilling fluid to remove bore hole cuttings and to otherwise perform functions related to drilling fluids. In many situations, what is generally referred to as a "drilling fluid" actually may be utilized with either no modification or only minor modification as a fluid for use in conjunction with completing or working over a subterranean well. In this connection, utilization of the phrase "drilling fluid", as used herein, contemplates the use of such fluid in completion and work-over operations in subterranean wells as well as in the initial drilling operations.
Although aqueous-based drilling fluids which utilize clear water, brine, saturated brine, or sea water as the primary liquid base constituent may be found to be dominant within some facets of the drilling industry, there is a considerable need for drilling fluids wherein a hydrocarbon liquid forms the primary liquid constituent, particularly in instances in which the drilling fluid is utilized in higher temperature wells which are drilled to greater depths than heretofore experienced.
Hydrocarbon-based drilling fluids normally are defined as invert emulsion, or water-in-oil emulsion drilling fluids. Such emulsions provide droplets of water which are typically dispersed in a continuous phase of oil. The oil, or continuous phase, typically will comprise a hydrocarbon such as mineral oil, diesel oil, crude oil, kerosene, or the like. The amount of such oil commonly used will be within the range of about 60 to 90 parts by volume and preferably within the range of about 70 to 90 parts by volume on the basis of 100 parts equaling the total liquid phase of the drilling fluid. The concentration of the selected hydrocarbon depends upon the particular application and earth formations for which the water-in-oil drilling fluid is to be utilized.
The dispersed liquid phase of the drilling fluid is commonly referred to as the "water phase" and may consist of fresh water, salt water, sea water, or saturated brine. Normally the presence of typical amounts of sodium chloride, calcium chloride, calcium carbonate, or calcium sulfate salts will have little effect on the stability of the emulsion which is typically produced. The water concentration will normally be in the range from between about 5 to 40 parts by volume and more commonly will be within the range of about 10 to 30 parts by volume on the basis of 100 parts equaling the liquid phase of the drilling fluid composition. As aforesaid, the exact concentration depends upon the particular application for which the invert emulsion drilling fluid is to be utilized.
The liquid hydrocarbons normally serve as a continuous liquid vehicle to be converted into a drilling fluid having desirable properties for the desired applications by adding various materials to thicken the fluid so that it will support cuttings and provide a low fluid loss when the fluid is subjected to filtration against a permeable formation and in addition to increase the density of the fluid. The fluids of the present invention are greatly improved for the aforesaid purposes and also have been found useful in certain other types of well-working operations. As is known, oil-bearing sands of low permeability are commonly subjected to extremely high fluid pressures in order to crack them open along bedding planes and the fractures so formed are held open by solid propping agents introduced with the fracturing fluid. In such use, it is desirable to employ an oil base fluid having low filtration loss, and in many cases it is also necessary to fill the annular space between the casing and the walls of the hole to facilitate most efficient production. It is also advantageous to use an oily fluid to minimize corrosion and to provide low fluid loss characteristics over lengthy time periods wherein the packing fluid remains in place. These operations involving drilling, fracturing, and packing are well-working operations; and the oil base well-drilling fluids, well-fracturing fluids, and well-packing fluids are all termed "oil base well-working fluids", as used in the following specification and claims.
In recent years, additives for the control of fluid loss have not been able to adequately control fluid loss at high bottom hole temperatures. This has resulted in increased additive consumption to maintain mud properties, thus increasing system costs. The fluids which are obtainable in accordance with our invention are characterized by extremely low filtrate loss after high temperature aging and the additives which are the subject matter of this invention are based on humic acid of such nature that undue thickening does not occur before fluid loss is lowered to an acceptable level.
Humic acid is a material of wide distribution being present in soils, peat, and soft coals; especially coals known as lignite or brown coal, as well in the mineral leonardite. While its precise chemical structure is not completely understood, it is a generally uniform material which represents a naturally occurring product of degradation, such as leaves, wood, and similar vegetable organic matter. It is an acid in which both carboxyl and phenolic hydroxyl groups contribute to its base combining ability. It is soluble in alkalis such as caustic soda and sodium carbonate, has a deep brown color, and is readily soluble in water when converted to alkali metal salts. Leonardite and lignite provide a common source of such humic acid which occurs in sizable deposits in the United States, especially in the western states.
U.S. Pat. Nos. 3,168,475 and 3,281,458 to Jordan et al relate to well drilling fluids in which substituted ammonium humates are utilized. The process employs such materials wherein the fluid is subject to loss of oil by filtration. U.S. Pat. No. 3,775,447 to Andrews et al relates to lignite products and compositions thereof, and more particularly to the reaction products of humic acid with long chain fatty acyl partial amides of polyalkylene polyamine for use in compounding oil base well working fluids. Also, U.S. Pat. No. 3,671,427 to Andrews et al relates to humic acid with long chain fatty acyl partial amines of a polyalkylene polyamine, the humic acid being reacted with the long chain alkyl ammonium cation for use in an oil base well-drilling fluid.
U.S. Pat. Nos. 3,538,071 and 3,671,428 to Kim relate to lignin derivatives for use in oil base drilling muds wherein an oxidized lignin is reacted with an amine to form a salt.
While the foregoing prior art discloses various amine salts of humic acid, none are produced by the method disclosed in the present application, and none have the chemical and physical characteristics of the subject reaction products for use as a filtration control additive for drilling fluids as first disclosed herein.
In co-pending application Serial No. 798,965, filed November 18, 1985, and entitled "Filtration Control Additive for Invert Emulsion Drilling Fluids and Method of Preparation", we disclosed the method of preparation and use of a pyrolyzed product derived from a finally divided humic acid-containing material together with a primary amine having an alkyl radical of 10 to 20 carbon atoms or a primary amine having one alkylsubstituted phenyl radical, with the alkyl radical having 10 to 20 carbon atoms. The derived product was obtained by reaction in a reaction chamber under controlled atmospheric conditions utilizing inert gas, carbon dioxide, or the like, under application of heat from about 185.degree. C. to the decomposition temperature of the resultant pyrolysis product. We have found that a satisfactory product may be obtained when the reactants are reacted within the specified temperature range, but in a vessel within which there is no application of pressure above atmospheric to the vessel interior during the reaction process. This alternative reaction procedure and resulting product have been found to be equally satisfactory when compared to the product derived from the reaction product wherein the reactants are introduced into a vessel which is caused to be exposed to an increase in pressure over atmospheric.